NO330367B1 - Gas processing plant for the recovery of propane and ethane. - Google Patents

Description

The invention relates to a gas processing plant for the recovery of a gas fraction from a supplied gas, and particularly relates to the recovery of propane and ethane.

Many natural gases and synthetically produced gases comprise many different hydrocarbons, and a number of methods and configurations are known in the art to produce commercially relevant fractions from such gases. Among other processes, cryogenic gas separation (see, e.g., US Patent Nos. 4,157,904, 4,690,702 or 5,275,005) has become a preferred method of gas separation.

In a typical gas separation process, a pressurized feed gas stream is cooled using a heat exchanger and as the gas cools, liquid condenses from the cooled gas. The liquids are then expanded and fractionated in a distillation column (e.g. a de-ethanizer or de-methanizer) to separate out residual components such as methane, nitrogen and other volatile gases as top vapor, from the desired C2, C3 and heavier components. In some configurations, uncondensed cooled feed gas is expanded to condense additional liquid, which can then be used as C2 and C3 absorbent in an absorber. Various improvements to the basic concept of cryogenic gas separation have been developed.

For example, US Patent No. 5,890,378 describes a system where (a) the absorber has a return flow, (b) where the de-ethanizer condenser provides ten I— backflows for both the absorber and the de-ethanizer, while the cooling requirements are met by the use of a turboexpander, and (c) where the absorber and deethanizer are operated at substantially the same pressure. Although the configuration advantageously reduces the capital cost of equipment associated with providing reflux for the absorption section and the de-ethanizer, propane recovery decreases significantly as the operating pressure in the absorber increases, especially at an overpressure above 3447 kPa, where separation of ethane from propane in the de-ethanizer -the ethanizer becomes increasingly difficult. Therefore, the system described in this patent is generally limited by the upper operating limit of the de-ethanizer pressure. Increasing the absorber pressure while maintaining desirable propane recovery becomes difficult, if not impossible, in this process configuration. Furthermore, operation of the absorber and deethanizer at an overpressure at or below 3447 kPa typically necessitates higher residual gas recompression, leading to relatively high operating costs.

In order to circumvent at least some of the problems associated with relatively high costs in connection with residual gas recompression, US patent no. 5,953,935 describes a plant configuration in which a further fractionation column is included. The absorber reflux in this plant configuration is produced by compression, cooling and Joule Thomson expansion of a discharge stream of feed gas. Although the configuration described in this patent generally provides improved propane recovery with essentially no increase in horsepower for the plant's residual compression, propane recovery decreases significantly as the operating pressure in the absorber rises, especially at overpressures above approx. 3447 kPa. Furthermore, ethane recovery using such known systems designed for propane recovery is usually limited to approx. 20% recycling.

In order to improve ethane recovery with a low C02 content in the ethane product, US patent no. 6,182,469 describes a tower reboiling scheme where one or more liquid tower distillation streams from a point higher in the absorber are used to drive off unwanted components (e.g. e.g., carbon dioxide in a de-methanizer). This scheme typically requires over-stripping of the ethane product, and CO2 removal is generally limited to approx. 6%. Furthermore, additional CCM iron using this process will significantly reduce ethane recovery and increase power consumption. Furthermore, and especially if the ethane product is used for chemical production, the product in this configuration typically requires further treatment to remove CO2 to or below a level of 500 ppmv, which often requires significant capital and operating costs.

Although there are various configurations and processes for improving propane and ethane recovery known in the art, all of these, or nearly all, are associated with one or more disadvantages. There is therefore still a need to provide improved methods and compositions for high propane recovery processes and configurations.

The present invention relates to configurations for a gas processing plant comprising an absorber with reflux 103 which is operated at a first pressure, while producing a bottom product stream 7 and receiving a

raw material and an absorber reflux stream 19;

- a distillation column 106 fluidly connected to the absorber 103, where the feed stream 11 is received in the column, and a distillation column overhead stream 13 is produced, and where the column is operated at a second pressure which

is at least 689 kPa lower than the initial pressure; and

- where at least a portion of the bottom product stream 7 is expanded and provides cooling for at least one of the absorber reflux stream 19 and the distillation column feed stream 11; and - where the distillation column overhead stream 13 is separated into a fluid portion 16 which provides reflux for the distillation column 106, and a

gaseous portion 15 which is liquefied and provides the absorber return flow 19.

In one embodiment, the distillation column 106 comprises a de-ethanization column, the feedstock has an overpressure of between 6895 kPa and 13790 kPa, and is expanded in a turbine expander 102. The bottoms product for the absorber is expanded in a range of 689 - 1724 kPa, thereby cooling the product to a temperature between -70.6°C and -87.2°C. It is also assumed that the cooled and expanded bottom product stream 8 is then fed as distillation column feed stream 11 into the distillation column 106, and it is further assumed that the expanded bottom product stream can further provide cooling for a distillation column reflux stream 13.1 a particular embodiment, the distillation column produces an overhead stream 13 which is compressed , is cooled and fed into the absorber 103 as absorber return flow 19.

In another embodiment, the distillation column comprises a de-ethanizer column, the raw material has an excess pressure of between 3792 kPa and 5516 kPa, and is not expanded in a turbine expander. The bottom product in the absorber 103 is expanded in a range of 689 - 1724 kPa, which cools the product to a temperature between -45.6°C and -56.7°C. It is also assumed that the cooled and expanded bottoms product stream is then fed as the distillation column feed stream 11 into the distillation column 106, and that at least a proportion of the raw material is fed into a lower section of the distillation column 106. 1 a further considered aspect is an external cooling connected to the distillation column 106 and the exchanger for added material.

In a still further embodiment, the distillation column 106 comprises a de-methanizer, the raw material is at an excess pressure of between 6895 kPa and 13790 kPa and is expanded in a turbo expander 102. It is also assumed that in such configurations the absorber bottom product is expanded in a range of 689 - 1724 kPa, whereby the bottom product stream is cooled to a temperature of between -70.6°C and -87.2°C. It is further assumed that the expanded bottom product 8 is fed as distillation column feed stream 11 into the distillation column 106, where the distillation column produces a distillation column top stream 13 which is compressed, cooled and fed into the absorber 103 as absorber reflux stream 19, and that the distillation column produces a distillation column product stream comprising no more than 500 ppm carbon dioxide. In particular aspects, the feedstock is split into a first portion and a second portion, and an external cooling device cools at least a portion of the first portion, and at least one sideboiler 116 located in the upper section of the distillation column 106 (ie, which is fluidly connected to the de-methanizer between a top plate and a position eight plates below the top plate), provides reboiling of the distillation column 106, provides heat for stripping CO2 from the de-methanizer product stream, and provides further cooling of the first portion of the feedstock.

Various purposes, features, aspects and advantages of the present invention will be made clear in the following detailed description of preferred embodiments of the invention, together with the accompanying drawings. Fig. 1 is a schematic drawing of an example of a gas processing plant for propane recovery according to the prior art. Fig. 2 schematically shows an example of the configuration of a gas processing plant for propane recovery with a turboexpander, a supply gas overpressure of approx. 8963 kPa and a de-ethanizer as distillation column. Fig. 2A is a graphic representation showing a heat composite curve (heat composite curve) for heat exchanger 100 in a plant configuration according to fig. 2. Fig. 3 is a schematic representation of yet another example of gas processing plant for ethane recovery in accordance with prior art. Fig. 4 is a schematic representation of a further example of configuration for a gas processing plant for ethane recovery with a turboexpander, a supply gas overpressure of approx. 8963 kPa and a de-methanizer as distillation column. Fig. 4A is a graphical representation showing a heat composition curve for heat exchanger 100 in a plant configuration according to fig. 4. Fig. 4B is a graphical representation showing a heat composition curve for heat exchanger 116 in a plant configuration according to fig. 4. Fig. 5 schematically shows yet another example of configuration for a gas processing plant without a turboexpander, a supply gas overpressure of approx. 5171 kPa and a de-ethanizer as distillation column. Fig. 6 schematically shows an example of configuration for a gas processing plant where the reflux absorber and the distillation column are configured in a single tower.

The inventors discovered that high propane recovery (ie, at least 95%) from a feed gas with a pressure that is relatively high (eg between about 6895 kPa gauge and 13790 kPa gauge) to relatively low (eg between about 3792 kPa overpressure and 5516 kPa overpressure) can be accomplished by operating an absorber in a gas processing plant at a significantly higher pressure than a distillation column (e.g. a de-ethaniser) and where the absorber bottoms product is expanded to provide cooling of the absorber reflux stream and/ or the distillation column feed. The inventors have further discovered that such configurations can also be used to significantly increase ethane recovery from relatively high pressure feed gas and to significantly remove CO2.

More particularly, the inventors envision a gas processing plant comprising a reflux absorber operated at a first pressure, producing a bottoms product stream and receiving a feedstock and an absorber reflux stream. Possible configurations further include a distillation column fluidly connected to the absorber receiving a distillation column feed stream and operated at a second pressure, which is at least 689 kPa lower than the operating pressure of the absorber, wherein at least a portion of the bottoms product stream is expanded and provides cooling of the absorber reflux stream and/or the distillation column feed stream.

Fig. 1 according to prior art depicts a known configuration for a propane recovery plant where a supply gas flow 1 at an overpressure of approx. 8963 kPa is cooled in a heat exchanger 100, separated into a gas and a liquid phase, and where the gas phase is then expanded in a turboexpander 102 and fed into the absorber 103, which is operated at an overpressure of approx. 3103 kPa. The liquid phase (if one exists) is Joule-Thomson (JT) expanded, and is fed directly into a lower part of the absorber. The bottom product in the absorber is pumped by means of pump 104 through heat exchanger 100, and the heated bottom product is then fed into the de-ethaniser.

The absorber 103 has a return flow using cooled de-ethanizer top flow 14, where the cooling of the return flow is provided by the top steam from the absorber, which is further heated in heat exchanger 100 before recompression in the recompressor 112 and subsequent residual gas compressor 113. Absorber 103 further provides return flow 17 which is introduced in the de-ethanizer by means of pump 108. Liquid product stream 12 exits the de-ethanizer with a propane recovery that is typically over 95%.

In contrast, a particularly preferred configuration of a gas processing plant for propane recovery as depicted in FIG. 2 an absorber 103 with return flow and which is operated at an overpressure of approx. 4068 kPa and a de-ethanizer 106 which is operated at an overpressure of about 2827 kPa, while feed gas stream 1 has an overpressure of about 8963 kPa. The supply gas stream 1 is cooled in heat exchanger 100 and separated in a separator 101 into a liquid portion 5 and a gas portion 4. The liquid portion 5 (if one is present) is fed into the absorber 103, while the gas portion 4 is expanded in a turboexpander 102 to the level of the operating pressure in the absorber. Expanded gas portion 6 is then fed into a lower section of the absorber 103. The absorber 103 receives reflux stream 19, which is provided by the top stream 13 from the de-ethanizer 106. The top stream 13 is cooled in a heat exchanger 105, and separated in a separator 107 into a gas phase 15 and a liquid phase 16. Liquid phase 16 is pumped back to the de-ethanizer which de-ethanizes-to-reflux by means of pump 108, while gas phase 15 is compressed in compressor 111 and cooled in heat exchanger 100 before entering the absorber as reflux stream 19.

The absorber bottom flow 7 is expanded in the JT valve 104, whereby the pressure is lowered to a degree of approx. 1241 kPa and significantly cools the bottom residual flow. The cooled absorber bottom stream 8 is then used as a coolant in the heat exchangers 100 and 105 before it enters de-ethanizer 106 which de-ethanizes feed stream 11. Absorber top stream 9 is heated in heat exchanger 100 and recompressed in recompressor 112 (which is operationally connected to the turboexpander). Recompressed peak flow 21 is further compressed in residual gas compressor 113 and fed into a residual gas pipeline. De-ethanizer-bottom stream-but 12 provides liquid product with a propane recovery of at least 99%.

As far as the feed gas flows are concerned, a number of natural and

synthetic feed gas streams to be considered suitable for use in connection with the teaching presented herein, and particularly preferred feed gas streams include natural gases, refinery gases and synthetic gas streams from hydrocarbon materials such as naphtha, coal, oil, lignite, etc. Consequently, the pressure for suitable feed gas streams vary considerably. Generally, however, it is preferred that appropriate supply gas overpressures for plant configurations according to fig. 2 will generally be in the range between 6895 kPa and 13790 kPa, and that at least a proportion of the raw material is expanded in a turboexpander to provide cooling and/or power for the residual gas recompression.

Depending on the pressure of the feed gas and the amount of feed gas expansion in the turboexpander, the operating pressure of the absorber may vary in the range between 3449 kPa and 5518 kPa overpressure, more preferably between 3449 kPa and 5173 kPa overpressure, and most preferably between 3794 kPa and 4828 kPa overpressure . It will thus be particularly preferred that the bottom product stream leaves the absorber at a significant pressure, and that cooling can be provided by expanding the bottom product stream to a lower pressure. In a particularly contemplated aspect, expansion of the bottom product stream reduces the bottom product stream pressure in a range from about 689 kPa to approx. 1724 kPa and more preferably in a range from approx. 1035 kPa to 380 kPa. It is thus conceivable that the absorber is operated at a pressure which is at least 689 kPa higher than the pressure of the distillation column; however, alternative pressure differences are also possible, and include absorber pressure differences of less than 689 kPa (e.g., between 345 and 683 kPa, and even less), and in particular include absorber pressure differences of more than 689 kPa (e.g., between 697 kPa and 1034 kPa, more preferably between 1041 kPa and 1724 kPa, and even higher).

It is therefore preferable that the temperature in the expanded bottom product stream will be in a range of approx. -70.6°C to -87.2°C. It is therefore assumed that the expanded bottoms product stream can further provide cooling for various streams within the gas processing plant, and it is particularly assumed that the expanded bottoms product stream further cools a distillation column overhead stream and an absorber return. It is further assumed that the expanded bottom product stream can be fed into the distillation column in different positions; however, it is particularly preferred that the expanded bottom product stream is fed into the distillation column at a position below the reflux feed point (eg at least three plates below the top plate in the distillation column).

In the case of the distillation column, it is particularly preferred that the distillation column produces a distillation column overhead stream which is compressed, cooled and fed into the absorber as the absorber reflux stream, thereby providing a particularly lean stream (stream 13 containing 64 mol% methane and 33 mol% ethane) which can be used to recover the propane and heavier components from the expanded feed gas streams. Considered configurations according to fig. 2 receives a feedstock comprising propane and provides a distillation column product stream comprising at least 95% of the propane in the feedstock.

In another particularly preferred aspect of the present invention, a gas processing plant as depicted in fig. 5 an absorber 103 with return flow which is operated at an overpressure of approx. 4964 kPa and a de-ethanizer 106 which is operated at an overpressure of approx. 3447 kPa, while the supply gas flow 1 has an overpressure of approx. 5240 kPa. The supply gas stream 1 is separated in separator 101 into a liquid portion 5 and a gas portion 2. The liquid portion JT is expanded in JT valve 115, and is fed directly into the de-ethanization column 106. The gas portion 2 is cooled in a heat exchanger 100, and the cooled gas portion 6 is fed then into absorber 103 without expansion in a turbo expander. The absorber 103 receives reflux stream 19, which is provided by the overhead stream 13 from the reflux vessel 102 of the de-ethanizer 106. The de-ethanizer overhead stream 13, coupled with an external cooling stream 109, and absorber overhead vapor stream 9 are used to cool feed stream 2 in exchanger 100. De-ethanizer peak stream 13 is heated to ambient temperature in exchanger 100 by means of the feed stream in exchanger 100, and then compressed in a compressor to stream 18. Compressor output stream 18 is cooled in an air-cooled exchanger 114, and then further cooled in heat exchanger 105 with absorber bottom flow 8 before it enters the absorber as return flow 19.

The absorber bottom flow 7 is expanded in the JT valve 104, so that the pressure is thereby lowered by approx. 1448 kPa, and the absorber bottom stream is cooled significantly from -43.9°C to -61.7°C. The expanded and cooled absorber bottom stream 8 is then used as a coolant in the heat exchanger 105 before it enters de-ethanizer 106 which de-ethanizer feed stream 11. Absorber top stream 9 is heated in the heat exchanger 100, and fed into the residual gas pipeline without recompression. The de-ethanizer bottom stream 12 provides liquid product with a propane recovery of at least 95%.

When it comes to the type and chemical composition of the supply gas, the same considerations apply as those described above. In plant configurations according to fig. 5, however, the supply gas has an overpressure of between approx. 3792 kPa and approx. 5516 kPa, and most preferably between approx. 4137 kPa and approx. 5,171 kPa overpressure. In particular, it should be understood that operating the absorber at a higher pressure makes it possible to feed the supply gas into the absorber without it passing through a turboexpander. The pressure in the absorber bottom product (which is preferably rich in methane) can therefore be advantageously used for cooling different streams in the plant.

It is assumed that the absorber bottom product flow is expanded to reduce the bottom product flow pressure in an area of approx. 345 kPa to approx. 2423 kPa, and more preferably in a range of approx. 689 kPa to approx. 1724 kPa. It is therefore expected that the bottom product stream will have a temperature between -34.4°C and -62.2°C, and more typically between approx. between -45.6°C and -56.7°C. Without limiting the present invention, it is generally assumed that the expanded bottoms product stream is introduced as a distillation column feed stream into the distillation column below the top of the distillation column, and it is preferred that the expanded bottoms product stream is introduced into the distillation column at a position at least three plates below a top plate in the distillation column. As regards the liquid portion of the feed gas, it is generally preferred that at least a portion of the feed gas is introduced into a lower section of the distillation column.

It is further to be understood that during propane recovery, the absorber bottoms are used after they have been used to cool the absorber top return, further (if residual cooling is available) to cool the de-ethanizer top vapor which provides return to the de-ethanizer. The heated absorber bottom product stream at approx. -34.4°C to approx. -45.6°C is fed to a feed plate located at least 3 plates from the top of the de-ethanizer. This arrangement improves the overall fractionation performance of the de-ethanizer by providing reflux and additional rectification while utilizing cooling content of the JT of the absorber bottoms. The de-ethanizer is operated at a peak temperature between -28.9 and -48.3°C.

As regards the de-ethanizer, it should be understood in particular that the de-ethanizer produces a top stream which is cooled and fed into the absorber as absorber-to-reflux stream, thereby providing a particularly lean stream (stream 13 containing 75 mol% methane and 25 mol % ethane) and which can be used to recover the propane and heavier components from the feed gas stream. Thus, the configurations according to fig. 5 a feedstock comprising propane, and providing a distillation column product stream comprising at least 95% of the propane in the feedstock.

In yet another further contemplated aspect of the invention, further configurations can be envisaged used in a gas processing plant for ethane recovery from a feed gas. Fig. 3 shows a configuration in accordance with prior art where a supply gas stream 1 at an overpressure of approx. 8963 kPa is cooled and separated into a gaseous portion 4 and a liquid portion 5. The gaseous portion is split into two streams, and the first stream is cooled and JT expanded, while the second stream is passed through a turboexpander. Both streams are then fed into different places in the de-methanizer. The de-methanizer is turned at an overpressure of approx. 2965 kPa. The de-methanizer overhead product provides cooling for the first stream and is recompressed by the turboexpander and further compressed by the tail gas compressor before exiting the plant as tail gas. Typically, the ethane recovery is approx. 80%, and the COH content in the ethane product is approx. 2 to 6%.

In contrast, an ethane recovery plant with configurations according to the present invention as shown in fig. 4, an absorber 103 with return flow and which is operated at an overpressure of approx. 4068 kPa and a de-ethanizer 106 which is operated at an overpressure of approx. 3103 kPa, while the supply gas stream 1 has an overpressure of approx. 6963 kPa. Supply gas flow 1 is split into a first portion 2a and a second portion 2b. The first portion 2a is cooled in heat exchanger 100 and the second portion 2b is cooled in heat exchanger 116. The respective cooled supply gas streams 3a and 3b are combined and separated in a separator 101 into a liquid portion 5 and a gas portion 4. The liquid portion 5 (if a as it occurs) is fed into the absorber 103 after JT expansion in the JT valve 115, while the gaseous portion 4 is expanded in a turboexpander 102 to the level of the operating pressure for the absorber 103. The expanded gaseous portion 6 is then fed into a lower part of the absorber 103. The absorber 103 receives a reflux stream 19, which is provided by the de-methanizer overhead stream 13 from the de-methanizer 106. The overhead stream 13 is separated in a separator 107 into a gaseous phase 15 and a liquid phase 16. Liquid phase 16 is pumped to the de-methanizer which de-methanizer reflux via pump 108, while gaseous phase 15 is compressed in compressor 111 and cooled in heat exchanger 100 before entering the absorber as reflux st escape 19.

Absorber bottom flow 7 is expanded in JT valve 104, thereby lowering the pressure to a degree of approx. 758 kPa and significantly cools the absorber bottom flow. The cooled absorber bottom stream 8 is then used as a coolant in the heat exchanger 100 before it enters the demethanizer 106 which demethanizes feed stream 11. The absorber top stream 9 is heated in the heat exchanger 100 and recompressed in the recompressor 112 (which is operationally connected to the turboexpander) . Re-compressed top flow 21 is further compressed in a residual gas compressor 113 and fed into a residual gas pipeline. De-methanizer bottom stream 12 provides liquid product with an ethane recovery of at least 69.0% and a CO 2 content of no more than 500 ppm. Two sideboilers, located in the top section of the de-methanizer, extract liquid distillate streams 109A and 109B. These streams are fed to the distillation column and provide heating work to remove the bulk of the CO2 from the liquid product, and further provide cooling of the first portion of the feedstock by streams 109A and 109B. The rest of the CO2 is removed in the bottom digester 110.

Suitable supply gases are assumed to have an excess pressure of between 6895 kPa and 13790 kPa. It is therefore preferred that at least a portion of the supply gas is expanded in a turboexpander. Additional cooling is provided by expanding the bottoms stream in a range of 689-1724 kPa. It is therefore assumed that the expanded bottom product stream has a temperature between -70.6°C and -87.2°C.

With regard to the de-methanizer, it should be understood in particular that the de-methanizer column produces an overhead stream which is compressed, cooled and fed into the absorber as absorber return stream, and therefore constitutes a particularly lean stream (stream 13 containing over 90 mol% methane ) and which can be used to recover ethane and heavier components from the expanded feed gas streams. The configurations according to fig. 4 receives a feedstock comprising ethane and propane and provides a distillation column product stream comprising at least 60% of the ethane and 95% of the propane in the feedstock.

In particular, it should be noted that the configurations according to fig. 4 can be used for recovery of up to 75% ethane without a significant increase in capital and operating costs for ethane recovery if the system can be used for high propane recovery according to fig. 2.1 a particularly suitable configuration, the feed to the de-methanizer is directed to a plate located at the top of the de-methanizer, and the top reflux condenser 105 in fig. 2 can be converted for use as a side boiler 116 for the de-methanizer of FIG. 4. Additional side boilers and external cooling can be used to improve the overall energy output. The de-methanizer overhead reflux system is bypassed in this operation, and the de-methanizer is now operated as a digester (compared to a fractionator during propane recovery). The basic equipment design and arrangement in the upstream system has been retained as in fig. 2, but with a lower operating temperature. The absorber on top is then operated at a lower temperature of approx. -73.3°C to approx. -90.0°C, and the temperature of the starting material of the de-methanizer is at a lower temperature of approx. -73.3°C to approx. -84.4°C.

It should further be understood that the previously known recovery plants designed for propane recovery can recover ethane in a range of 20% to 40%. In contrast, configurations according to the present invention, with small changes in operating and process parameters, can be used economically for ethane recovery up to 75%. Furthermore, the ethane produced in previously known recovery plants designed for ethane recovery usually contains 2-6% CO2.1 In contrast, configurations according to the present invention will allow ethane recovery where C02 is present in the ethane in an amount of less than 500 ppm, and more typically less than 350 ppm.

Regarding all the components of the intended configurations (e.g. heat exchangers, pumps, valves, compressors, expanders, absorbers with reflux, de-ethanizers, etc.), it is to be understood that all known and commercially available components are suitable for use in connection with the teachings presented herein. Furthermore, it is generally considered that configurations according to the present invention can find wide applicability for gas plant purposes where high propane recovery is desirable, and where supply gas is available at an overpressure of more than 3792 kPa. Furthermore, such configurations can advantageously reduce equipment and operating costs, especially where turboexpander technology would make it necessary to compress supply gas and/or residual gas. For gas plant purposes where energy costs are relatively high and propane value compared to fuel value is marginal, preferred design configurations are considered to greatly reduce overall energy compression costs by operating the absorber at between 4137 and 5171 kPa overpressure while maintaining propane recovery of between 85% and 95%. Furthermore, it should be understood that by combining the reflux absorber and de-ethanizer in a single column as shown in fig. 6, then the requirements for the total construction area can be reduced, which can provide significant cost savings in the design of modules and platforms.

Examples

Operation of gas processing plants according to Figures 1, 2, 3, 4, and 5 was computer simulated using process simulator HYSYS, and Tables 1, 2, 3, 4, and 5, which are attached, summarize examples of component flow, pressure and temperatures in the configurations as shown in fig. 1-5.

Furthermore, calculations were carried out to present the heat composition curve for heat exchanger 100 in the plant configuration according to fig. 2. The heat exchanger 100 in the plant configuration according to fig. 4 and the side heat exchanger 116 in the plant configuration according to fig. 4, and the results are depicted respectively in Figures 2A, 4A, and 4B. The energy efficiencies of these inventions are very high, which is demonstrated by the relatively close temperature approximations of these composite curves.

Specific embodiments and applications of high propane recovery processes and configurations have thus been described. However, it will be clear to those skilled in the art that many more modifications in addition to those already described are possible without departing from the inventive idea of the invention. When interpreting both the description and the requirements, all designations should be understood in the broadest possible way in accordance with the textual context.

Claims (28)

1. Gas processing plant for the recovery of propane and ethane, characterized in that it comprises: an absorber with reflux (103) operated at a first pressure, under producing a bottom product stream (7) and receiving a raw material and an absorber reflux stream (19); a distillation column (106) fluidly connected to the absorber (103), where the feed stream (11) is received in the column and a distillation column overhead stream (13) is produced, and the column is operated at a second pressure which is at least 689 kPa lower than the first pressure; and - where at least a portion of the bottom product stream (7) is expanded and provides cooling for at least one of the absorber reflux stream (19) and the distillation column feed stream (11); and wherein the distillation column overhead stream (13) is separated into a fluid portion (16) which provides reflux for the distillation column (106), and a gaseous portion (15) which is liquefied and provides the absorber reflux stream (19). 2. Gas processing plant according to claim 1, characterized in that the distillation column (106) comprises a de-ethanizer column. 3. Gas processing plant according to requirement 2, characterized in that the raw material is at an overpressure of between 6895 kPa and 13790 kPa. 4. Gas processing plant according to requirement 3, characterized in that at least one portion of the raw material is expanded in a turboexpander (102). 5. Gas processing plant according to claim 3 or claim 4, characterized in that the bottom product flow (7) has a pressure and that expansion of the bottom product flow (7) reduces the bottom product flow pressure to a range of 689 - 1724 kPa. 6. Gas processing plant according to requirement 3, characterized in that the expanded bottom product stream (8) has a temperature between -70.6°C and -87.2°C. 7. Gas processing plant according to requirement 3, characterized in that the expanded absorber bottom product stream (8) is fed as distillation column feed stream (11) into the distillation column (106) in a position that is at least three plates below a top plate in the distillation column (106). 8. Gas processing plant according to claim 3 or claim 5, characterized in that the expanded bottom product stream (8, 10) further provides cooling of a distillation column top stream (13). 9. Gas processing plant according to requirement 3, characterized in that the distillation column (106) produces a distillation column overhead stream (13) which is compressed, cooled and fed into the absorber (103) as absorber reflux stream (19). 10. Gas processing plant according to claim 3, characterized in that the raw material comprises propane, and that the distillation column (106) produces a distillation column product stream (12) comprising at least 95% of the propane in the starting material. 11. Gas processing plant according to claim 2, characterized in that the raw material is at an overpressure of between 3792 kPa and 5516 kPa. 12. Gas processing plant according to claim 11, characterized in that the raw material is fed into the absorber (103) without going through a turboexpander (102). 13. Gas processing plant according to claim 11, characterized in that the bottom product flow (7) has a pressure, and that expanding the bottom product flow (7) reduces the bottom product flow pressure to a range of 689 - 1724 kPa. 14. Gas processing plant according to claim 11, characterized in that the bottom product stream (7) has a temperature of between -45.6°C and -56.7°C. 15. Gas processing plant according to claim 11, characterized in that the expanded bottom product stream (8) is fed as the distillation column feed stream (11) into the distillation column (106) at a position which is at least three plates below a top plate in the distillation column. 16. Gas processing plant according to claim 11, characterized in that at least part of the raw material is fed into a lower part of the distillation column (106). 17. Gas processing plant according to claim 11, characterized in that it further comprises an external cooling device connected to the distillation column (106). 18. Gas processing plant according to claim 1, characterized in that the distillation column (106) comprises a de-methanizer. 19. Gas processing plant according to claim 18, characterized in that the raw material is at an overpressure of between 6895 kPa and 13790 kPa. 20. Gas processing plant according to claim 18, characterized in that at least part of the raw material is expanded in a turboexpander (102). 21. Gas processing plant according to claim 18, characterized in that the bottom product stream (7) has a pressure, and that expanding the bottom product stream (7) reduces the bottom product stream pressure to a range of 689 - 1724 kPa. 22. Gas processing plant according to claim 18, characterized in that the expanded bottom product stream (8) has a temperature between -70.6°C and -87.2°C. 23. Gas processing plant according to claim 18, characterized in that the expanded bottom product stream (8) is fed as distillation column feed stream (11) into the distillation column. 24. Gas processing plant according to claim 18, characterized in that the distillation column (106) produces a methane-rich distillation column overhead stream (13) which is compressed, cooled and fed into the absorber (103) as absorber reflux stream (19). 25. Gas processing plant according to claim 18, characterized in that the distillation column (106) produces a distillation column product stream (12) comprising no more than 500 ppm carbon dioxide. 26. Gas processing plant according to claim 18, characterized in that the raw material is split into a first portion and a second portion, and where an external cooling cools at least part of the first portion. 27. Gas processing plant according to claim 26, characterized in that it further comprises at least one side reboiler connected to the distillation column (106), the at least one side reboiler (116) being fluidly connected to the de-methanizer between a top plate and a position eight plates below the top plate, and providing heating energy for driving off CO 2 from a de-methanizer product stream, provides reboil for the distillation column (106) and provides further cooling of the first portion of the feedstock. 28. Gas processing plant according to claim 1, characterized in that the absorber and distillation column (106) are configured in a single tower configuration.